Re: healp reading / writing binary strings.

Robert Klemme wrote:
On 18.06.2007 03:52, Melissa Silas wrote:
What exactly kind of format is that?
Um, how can we know what format this is? I mean, you came up with that
string. The definition above just uses octal escapes. You can as well
have hex codes:

irb(main):013:0> "\x21\x20\x40"
=> "! @"

> How do I parse it / read binary
data from it?

Depends on what you want to do with it. If you want to access bytes you
can simply do this

irb(main):014:0> s = "\t\001"
=> "\t\001"
irb(main):015:0> s[0]
=> 9
irb(main):016:0> s[1]
=> 1

If you want bits you can do

irb(main):017:0> s.unpack "b*"
=> ["1001000010000000"]
irb(main):018:0> s.unpack "b8b8"
=> ["10010000", "10000000"]
irb(main):019:0> s.unpack "b4*"
=> ["1001"]
irb(main):020:0> s.unpack "b4b4b4b4"
=> ["1001", "1000", "", ""]
irb(main):021:0> s.unpack "b4b4b"
=> ["1001", "1000", ""]
irb(main):022:0> s.unpack "b4b4"
=> ["1001", "1000"]

Please see #unpack docs for more info.

> And how can I write the same type of string from say an
array? ["foo","bar"]?

"Write from an array"? I don't understand what you mean. If you want to
put it into an array, you can simply do

irb(main):023:0> ["foo", "\tbar\n"]
=> ["foo", "\tbar\n"]

Kind regards

robert


Thanks that helps.. Couple more questions..

for this example:
s = "\t\001"
puts s[0] -> 9
How does \t come out as 9? Is that the tab char which in turn is the
number 9 in ascii table?

for this example:
s = "\001"
Ok so now I know this is octal, does the octal value I supply correspond
to the ascii table as well?

for this example:
s = "\x01"
for hex, does the hex value I supply correspond to the ascii table as
well?

Thanks for the help. This is helping me understand this a bunch..

-Melissa

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